Post-depositional modification of atmospheric dust on a granite building in central Rio de Janeiro: implications for surface induration and subsequent stone decay

Extensive contour scaling of a 200 year old granite church is associated with the breaching of an apparently iron-rich crust and the widespread deposition of atmospheric dust within the canyon-like streetscape of Rio de Janeiro. Contemporary dust, accumulated dust from within the a depression on the building surface, the surface crust and the underlying granite are examined by a combination of total element analysis and sequential extraction, X-ray diffraction and energy dispersive X-ray fluorescence. Results indicate an increase in total organic carbon and a marked decrease in pH within the accumulated dust, and a rapid mobilization of anions and cations from the water-soluble and carbonate phases. It is considered that the latter is linked to salt accumulation within and eventual salt weathering of the granite. Post-depositional alteration of the dust is also linked with the de-silicification of clay minerals (Illite to kaolinite) and the loss of silica from the amorphous Fe/Mn phase of the accumulated dust under the initially saline and progressively more acidic conditions experienced at the stone - atmosphere interface. This mobilization of silica is associated with the formation of what is, in effect, a thin silica-rich surface crust or glaze. Within the glaze, assessory amounts of extractable iron are concentrated within the amorphous and crystalline Fe/Mn phases at levels that are significantly elevated with respect to the underlying granite, but much lower than the equivalent phases of the accumulated dust from which it is principally assumed to derive. The protection afforded to the stone work by the crust is not, however, permanent and within the last 15 years it has been possible to observe a rapid increase in the surface delamination of the church close to street level.

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX.

We report calculations of energy levels, radiative rates and electron impact excitation cross<br/>sections and rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX. The grasp<br/>(general-purpose relativistic atomic structure package) is adopted for calculating energy levels<br/>and radiative rates. To determine the collision strengths and subsequently the excitation rates,<br/>the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line<br/>strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of<br/>each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the<br/>effective collision strengths obtained listed over a wide temperature range up to 107.4 K.<br/>Comparisons are made with similar data obtained from the flexible atomic code (fac) to<br/>highlight the importance of resonances, included in calculations with darc, in the<br/>determination of effective collision strengths. Discrepancies between the collision strengths<br/>from darc and fac, particularly for forbidden transitions, are also discussed. Additionally,<br/>theoretical lifetimes are listed for all the 49 levels of the above four ions.

Spectacles of military urbanism in online representations of the Elite Squad of the military police of Rio de Janeiro: a multimodal approach

This paper presents a multimodal analysis of online self-representations of the Elite Squad of the military police of Rio de Janeiro, the Special Police Operations Battalion BOPE. The analysis is placed within the wider context of a ���new military urbanism���, which is evidenced in the ongoing ���Pacification��� of many of the city���s favelas, in which BOPE plays an active interventionist as well as a symbolic role, and is a kind of solution which clearly fails to address the root causes of violence which lie in poverty and social inequality. The paper first provides a sociocultural account of BOPE���s role in Rio���s public security and then looks at some of the mainly visual mediated discourses the Squad employs in constructing a public image of itself as a modern and efficient, yet at the same time ���magical��� police force.